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Biomedical subjects

A W Schopper

Publications and source records attributed to A W Schopper.

10 recordsLinked to original sources
PubMed2003

Impact of muscle length during stretch-shortening contractions on real-time and temporal muscle performance measures in rats in vivo.

The objective of the present study was to investigate the impact of muscle length during stretch-shortening cycles on static and dynamic muscle performance. Animals were randomly assigned to an isometric (control, Con, n = 12), a short-muscle-length (S-Inj, 1.22-2.09 rad, n = 12), or a long-muscle-length (L-Inj, 1.57-2.44 rad, n = 12) group. The dorsiflexor muscles were exposed in vivo to 7 sets of 10 stretch-shortening contractions (conducted at 8.72 rad/s) or 7 sets of isometric contractions of the same stimulation duration by using a custom-designed dynamometer. Performance was characterized by multipositional isometric exertions and positive, negative, and net work before exposure, 6 h after exposure, and 48 h after exposure to contractions. Real-time muscle performance during the stretch-shortening cycles was characterized by stretch-shortening parameters and negative, positive, and net work. The S-Inj group recovery (force difference) was similar to the Con group force difference at 48 h, whereas the L-Inj group force difference was statistically greater at 1.39, 1.57, and 1.74 rad than the Con group force difference (P < 0.05). Negative work (P < 0.05) and net work (P < 0.05) were statistically lower in the S-Inj and L-Inj groups than in the Con group 48 h after exposure to contractions. Of the real-time parameters, there was a difference in cyclic force with treatment during the stretch-shortening cycles (P < 0.0001), with the L-Inj group being the most affected. Thus longer ranges of motion result in a more profound isometric force decrement 48 h after exposure to contractions and in real-time changes in eccentric forces.

Animals↗
PubMed2003

Modeling of time-dependent force response of fingertip to dynamic loading.

An extended exposure to repeated loading on fingertip has been associated to many vascular, sensorineural, and musculoskeletal disorders in the fingers, such as carpal tunnel syndrome, hand-arm vibration syndrome, and flexor tenosynovitis. A better understanding of the pathomechanics of these sensorineural and vascular diseases in fingers requires a formulation of a biomechanical model of the fingertips and analyses to predict the mechanical responses of the soft tissues to dynamic loading. In the present study, a model based on finite element techniques has been developed to simulate the mechanical responses of the fingertips to dynamic loading. The proposed model is two-dimensional and incorporates the essential anatomical structures of a finger: skin, subcutaneous tissue, bone, and nail. The skin tissue is assumed to be hyperelastic and viscoelastic. The subcutaneous tissue was considered to be a nonlinear, biphasic material composed of a hyperelastic solid and an invicid fluid, while its hydraulic permeability was considered to be deformation dependent. Two series of numerical tests were performed using the proposed finger tip model to: (a) simulate the responses of the fingertip to repeated loading, where the contact plate was assumed to be fixed, and the bone within the fingertip was subjected to a prescribed sinusoidal displacement in vertical direction; (b) simulate the force response of the fingertip in a single keystroke, where the keyboard was composed of a hard plastic keycap, a rigid support block, and a nonlinear spring. The time-dependent behavior of the fingertip under dynamic loading was derived. The model predictions of the time-histories of force response of the fingertip and the phenomenon of fingertip separation from the contacting plate during cyclic loading agree well with the reported experimental observations.

Bone and Bones↗
PubMed2002

Simulation of mechanical responses of fingertip to dynamic loading.

Extended exposure to mechanical vibration has been related to many vascular, sensorineural and musculoskeletal disorders of the hand-arm system, frequently termed 'hand-arm vibration syndrome' (HAVS). A two-dimensional, nonlinear finite element model of a fingertip is developed to study the stress and strain fields of the soft tissue under dynamic loading, that may be encountered while grasping and operating a hand-held power tool. The model incorporates the most essential anatomical elements of a fingertip, such as soft tissue, bone, and nail. The finger is assumed to be in contact with a steel plate, simulating the interaction between the fingertip and a vibrating machine tool or handle. The soft tissue is assumed to be nonlinearly visco-elastic, while the nail, bone, and steel plate are considered to be linearly elastic. In order to study the time-dependent deformation behavior of the fingertip, the numerical simulations were performed under ramp-like loading with different ramping periods and sinusoidal vibrations of the contacting plate at three different frequencies (1, 10, and 31.5 Hz). Owing to relatively large deformations of the soft tissue under specified static and dynamic loading, Lagrangian large deformation theory was applied in the present analysis. The effects of the loading rate and the frequency of the sinusoidal vibration on the time-dependent strain/stress distributions in the different depth within the soft tissue of the fingertip are investigated numerically. Our simulations suggest that the soft tissue of the fingertip experiences high local stress and strain under dynamic loading and the fingertip may separate from the vibrating contact surface due to the viscous deformation behaviour of the soft tissue. For a given deformation, the high frequency loading produces a higher stress in the tissues compared to that obtained at a low frequency loading. The present model may serve as a useful tool to study the mechanism of tissue degeneration under vibratory loading encountered during operation of hand-held power tools.

Computer Simulation↗
PubMed2002

A method for reducing adaptor misalignment when testing gloves using ISO 10819.

OBJECTIVES: International standard ISO 10819 was established in order to quantify the vibration attenuation characteristics of anti-vibration gloves. One problem that exists with the standard is possible misalignment of the palm adaptor that is placed underneath the test glove. If the adaptor becomes misaligned, the measured glove transmissibility will be lower than the actual value. A tri-axial accelerometer was installed in the adaptor and was used as the basis for providing visual feedback of the adaptor alignment to the test subjects. The objective of this study was to test the hypothesis that adaptor misalignment could be reduced by providing feedback to the test subjects. METHODS: Eight male volunteers (mean age 24.8 yr) were used in the study. Each subject performed two sets of tests: the standard ISO 10819 glove test and the modified version. Three different anti-vibration gloves were tested. Glove transmissibility and adaptor misalignment were calculated for each glove. A three-way analysis of variance was used to analyze the results. RESULTS: A comparison of the two testing methods showed that the modified glove testing method did reduce misalignment significantly, which, in turn, resulted in an increase in the measured glove transmissibility. CONCLUSIONS: The proposed method greatly improved the standard deviation of transmissibility and made the test results more consistent.

Adult↗
PubMed2001

Hand-transmitted vibration and biodynamic response of the human hand-arm: a critical review.

Hand-arm vibration syndrome (HAVS) has been associated with prolonged exposure to vibration transmitted to the human hand-arm system from hand-held power tools, vibrating machines, or hand-held vibrating workpieces. The biodynamic response of the human hand and arm to hand transmitted vibration (HTV) forms an essential basis for effective evaluations of exposures, vibration-attenuation mechanisms, and potential injury mechanisms. The biodynamic response to HTV and its relationship to HAVS are critically reviewed and discussed to highlight the advances and the need for further research. In view of its strong dependence on the nature of HTV and the lack of general agreement on the characteristics of HTV, the reported studies are first reviewed to enhance an understanding of HTV and related issues. The characteristics of HTV and relevant unresolved issues are discussed on the basis of measured data, proposed standards, and measurement methods, while the need for further developments in measurement systems is emphasized. The studies on biodynamic response and their findings are grouped into four categories based on the methodology used and the objective. These include studies on (1) through-the-hand-arm response, expressed in terms of vibration transmissibility; (2) to-the-hand response, expressed in terms of the force-motion relationship of the hand-arm system; (3) to-the-hand biodynamic response function, expressed in terms of vibration energy absorption; and (4) computer modeling of the biodynamic response characteristics.

Arm↗
PubMed1989

SPH-4 U.S. Army flight helmet performance, 1972-1983.

Injury data were obtained from the U.S. Army Safety Center for the occupants of U.S. Army aircraft who were both wearing aviator helmets and involved in duty-related aircraft accidents, for the period beginning on 1 January 1972 and ending 1 January 1983. The injury data were correlated with the physical condition of the involved helmets, examined by the authors under an Aviation Life Support Equipment Retrieval Program. Each helmet's performance was evaluated with regard to current injury prevention capabilities and potential improvements for future helmet design. For consistency, only the 208 SPH-4s in the data base were fully analyzed. Combat damaged helmets were excluded from this analysis.

Accidents, Aviation↗
PubMedDate not supplied

Analysis of skin deformation profiles during sinusoidal vibration of fingerpad.

Vibrotactile perception threshold measurement has been widely used to diagnose the severity of peripheral neuropathy associated with hand-arm vibration syndrome and sensory losses in stroke and diabetic patients. The vibration perception threshold is believed to be influenced by many factors, such as contact force and vibration frequency. The present study is intended to analyze, theoretically, the time-dependent deformation profile of skin surface, strain distributions within soft tissue, and response force of a fingertip when it is stimulated by a probe vibrating with a sinusoidal movement. A two-dimensional finite element model, which incorporates the essential anatomical structures of a finger: skin, subcutaneous tissue, bone, and nail, has been proposed to analyze the effects of vibration amplitude, frequency, and preindentation on the dynamic interaction between the fingerpad and vibrating probe. The simulation results suggest that the fraction of time over which the skin separates from the probe during vibration increases with increasing vibration frequency and amplitude, and decreases with increased preindentation of the probe. The preindentation of the probe has been found to significantly reduce the trend of skin/probe decoupling. The simulation results show reasonably consistent trends with the reported experimental data.

Adaptation, Physiological↗